To prevent an article from being fouled with finger prints, sebum, sweat, cosmetics, or food, an antifouling coating is often provided to the article such as lenses of eye glasses or sun glasses, displays of cell phones, personal digital assistants, portable musical players, liquid displays, CRT displays, plasma displays, and EL displays, optical mediums such as compact disks (CD) and digital versatile disks (DVD), and window glass.
Japanese Patent Application Laid-Open, hereinafter abbreviated as “JPA”, No. H09-137117, JPA No. 2000-143991 and JPA 2005-290323 describe a method of forming an antifouling coating by applying a perfluoropolyether having an alkoxysilyl group at an end. JPA H02-248480 and H06-184527 describe a method to form an antifouling coating layer comprising a fluoroalkylsilane compound on a glass plate surface. JPA H06-256756 describes a method to form an antifouling coating layer comprising a fluoroalkylsilane compound and a polysiloxane compound on a glass plate surface.
To apply the fluoroalkylsilane and the perfluoropolyether having a terminal alkoxysilyl group, they are usually dissolved in a solvent and then spin-coated on an object. However, due to their high fluorine contents, they are soluble only in limited solvents, mostly fluorinated solvents. Because such solvents are not miscible with water, hydrolysis of the fluoroalkylsilane or the perfluoropolyether is controlled by atmospheric moisture, proceeding slowly.
To solve this problem, JPA No. H10-204421 describes a method of surface reforming comprising the steps of surface-treating with a silane coupling agent having a polar group which agent is soluble in various solvents, and then reacting the polar group with a fluoroalkyl carboxylic acid halide or a perfluoropolyoxyalkyl carboxylic acid halide to fix the fluoroalkyl or perfluoro polyoxyalkyl group to the surface. The method requires two steps, which is troublesome and time-consuming. Further, halides formed in the second step are not desirable from the environmental viewpoint.
To promote hydrolysis of an alkoxysilyl group, a catalyst may be added to a coating composition. Examples of known catalysts for hydrolysis reaction include organic titanate such as tetrabutyl titanate and tetraisopropyl titanate; organic titanium chelate compounds such as titanium diisopropoxy bis(ethylacetoacetate); organic aluminum compounds such as aluminum tris(acetylacetonate) and aluminum tris(ethyl acetoacetate); organic zirconium compounds such as zirconium tetra(acetylacetonate) and zirconium tetrabutylate; organic tin compounds such as dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin di(2-ethylhexanoate), dioctyltin dilaurate, dioctyltin diacetate, and dioctyltin dioctoate; a metal salt of a carboxylic acid such as tin naphthenate, tin oleate, tin butylate, cobalt naphthenate, and zinc stearate; amine compounds and salts thereof such as hexyl amine and dodecyl amine phosphate; quarterly amine salts such as benzyl triethyl ammonium acetate; salts of lower fatty acids such as potassium acetate and lithium nitrate; dialkylhydroxylamine such as dimethylhydroxylamine and diethylhydroxylamine; organosilicon compound having a guanidyl group such as tetramethylguanidylpropyltrimethoxy silane; organic acids such as acetic acid and methanesulfonic acid, and inorganic acid.
However, these catalysts are insoluble or scarcely soluble in fluorinated solvents, so that catalytic efficiency of these catalysts is low. Moreover, metals contained in the catalysts remain in a cured coating layer to cause degradation of the coating layer.